According to the New York City Hospitality Alliance, the SLA classifies brunch as an "event," which allows it to hurdle the law. If you'd prefer to hear this in non-layman's terms, here's how the SLA explains it, in detail:

Serving unlimited drinks to a patron is prohibited under the Alcoholic Beverage Control law, and instances of over serving by our licensees will be investigated and prosecuted. However, there is a limited exception in the statute when the service of alcohol is incidental to the event, such as in the case of certain brunch specials.

Still, the SLA asks that businesses not serve patrons to the point that they're slurring or worse. That's fair, but at least clarity has been provided. Credit the media for forcing this to happen.